Method of cleaning steam



April 27, 1937. w. T. SHERMAN I METHOD OF.CLEANING STEAM Filed June 25,19:54

ORV P/PE MW mam ATTORNEY 7 moving these entrained atente pr. 11 5.1? MdWilliam '11. She i w r n, Wbury, N. .lL, agnor to Socony-Vacnnm on Compt lncorpora i ii New York, N. Y" a corporation of New York Applicationlie 23,- ldiid, Serial No. I32JW8 5 ilJlaiims.

The present invention relates to a mode of operation of equipment forwashing and drying steam, and particularly to an improved method ofcleaning steam by the treatment of the steam with water having a lowcontent of material capable of forming solid deposits.

The general field of the invention is the pro.- vision of a processcapable of removing entrained liquids and/or solid material from steam,and the more specific field in which the present inventionisparticularly applicable is that of rematerials from high pressuresteam.

The entrainment of liquid and/or solid materials in steam gives'rise toconsiderable dimculties in the operation of powerplants. The liquidsand/or solids may be entrained in the steam from a number of causes,such as foaming, prim ing and similar dimc'ulties of boiler operation,

and it is frequently possible for serious amounts of such impurities tobe present without foaming or priming, "probably from certain causeslater discussed. These impurities in the steam give rise to considerabledifllcultieatespecially noticeable when the steam from the boiler ispassed to a superheater, or when it is used in a turbine. In asuperheater, solid materials present in the steam fed to thesuperheater, are

deposited upon the interior of the super tubes, forming a dense andcompact scale which rapidly causes marked decreases in the heat transfercapacity of the superheater, and frequent shut-downs are required forcleaning. This solid material gives rise to considerable onlties inpipes and fittings used for distributing and controlling the steam, asit rapidly e es the inner walls of bends, etc., cuts the seat and discsof partially opened valves, and generallycauses the flowing stream ofsteam tube of what might be termed an. abrasive nature. If steamcarrying a considerable amount of entrained materials is used fordriving a steam turbine, .it is.

I ing material.

solids appear in a percentage relative to the total must be dismantledand cleaned. In either case, serious losses of operating time andusefulness of equipment are had. If suficient erosion has.

resulted, the turbine must necessarily be.rebuilt.

The presence of solids in steam, or of materials which will laterdeposit as solids, does not always appear to be the result of foaming,or priming. Foaming occurs when the concentration of certain materialsin the boiler water in the steaming drumis of such a nature that the Ifrothy steam'which apparently fills the steaming space and is carriedaway from the boiler. This condition is usually spoken of as priming,

and is a similar source of entrainment. A further source of entrainment,less well understood, isbelieved to be responsible for a considerableportion of the trouble due to carrying over solids or solid-formingmaterial in steam. Apparently when the boiler water hasa relatively highconcentration of dissolved solid-forming material, it may allowsumciently free disengagement of steam to avoid frothing or foaming, andthe steam coming from the boiler drum may be, for all practicalpurposes, dry, and yet contain a relatively high proportion of solids orsolid-formlit is frequently noted that these steam which is more or lessindependent of the amount of load or rate of application of load on theboiler, which would argue that they are not placed in the steam by anyaccident such as priming. Similarly, it has beennoted that theconcentration of solids in steamfrequently appears to be somewhatparallel to the concentrationof solid-forming material in the boilerwater. Probably the formation of these solids is due to some suchactionas the following: When a hubble of steam,bursts at the surface of theliquid, it throws a small portion of the highly concentrated boilerwater into the vapor space. ,This boiler water evaporates in the vaporspace without falling back to the liquid, and the solids which were insuch water are left within the .vapor as a more or less dry and finepowder, and

as such, are carried from the boiler with the steam. Whether or not thistheory as to how impurities'may be carried over is correct is not.known, but I have found that dry steammay functions to remove some ofthe impurities, it

frequently contain relatively high percentages of solid material capableof causing erosion, etc., or -of being deposited in superheaters or uponturbine blades, that I can remove such solid ma-. .terial by an actualwashing of the steam with a water of relatively low concentration ofsolids, and that the cleaning is not complete unless the wetting of theotherwise dry steam is complete. It-is important that the cleaning berelatively complete for, while the weight percentage of solids presentmay be minute, the potential cost and damage therefrom may be enormous,becoming especially aggravated with increases of system pressure, andthe problem of their substantially complete removal is therefore acuteand pressing. It is with a method for the solution of .such a problem ofsteam cleaning that this application has to do.

Prior methods of cleaning steam which attempt to solve this problem haveconsisted of various arrangements of baiiiing devices interposed withinthe steam space of the boiler in such a way that the steam must passthrough these baffles before it leaves the boiler, coupled with a sprayof boiler makeup waterwhich is distributed somewhat in the form of acurtain upon the entering side of the baflies. These devices have beenfound to be subject to serious disadvantages, the greatest being that itis quite diflicult to arrange the baflles and sprays so that there is atall times an assurance of positive contact between the steam to bescrubbed and the scrubbing spray. A further disadvantage is that theimpurities in the spraying water itself may be relatively concentrated,and, while such water may do so by replacing them with other impurities.Frequently also, the interaction of the spray and the baiiies. is suchas to cause deposit of the entrained solid material after wetting uponthe surfaces of the baflles, which quickly results in clogged baflles.and failure of means for removing steam from the boiler. A furtherserious disadvantage is that the-requirements of space within the boilercall for high steam velocity through the baffles, and the sprayingwater, after taking up material from the steam, frequently may be sweptoil the baflies by the action of the stream of vapors and returned tothe steam as an imall of the portions of the steam with a scrubbing Iagent. It is a further object to develop a process enabling the use of ascrubbing agent of low or relatively. low concentration of impuritiescapable of forming solids. A further object is to develop such a processin which the scrubbing agent, after contact with the steam, may bepositively and effectively removed therefrom. Another object is theprovision'of a process wherein the steam scrubbing may be carried outwithout derangement of the normal heat balances ofv the system. Afurther object is the devising of a process capable of performing therequired cleaning without being hampered by the requirements of spacewithin the steaming drum of the boiler, and which, in its preferredform, is carried on outside of the, drum. Otherobjects and advantageswill appear in the descrip tive matter following.

The process of this invention may be briefly described as that ofvigorously scrubbing steam with water of low solid concentration, in amanner which requires positive contacting of all of the steam with thescrubbing-water followed by the removal of the water with theimpurities,

1 In order that my process of steam cleaning and the' apparatus thereformay be more thoroughly understood, reference is now made to the drawingattached to and forming a part of this specification. In this drawing,Figure 1 is a diagrammatic representation of the preferred form of myinvention, while Figure 2 is a. diagrammatic showing of a variation inwhich the scrubbing device-is placed in the steaming space of theboiler.

In Figure 1 of the drawing, l indicates the steaming drum of a highpressure boiler, the tubes and other drums of the boiler not beingshown. 2 indicates the steam main leading from steam 'drum I to scrubber3. This pipe 2 enters scrubber 3 below a partition 4. In thispartitition 4 to a point well below water level 6. Other than for theopenings through tube 5 and tube 1, the partition 4 is imperforate. Theliquid storage space in the bottom of the scrubber 3 is supplied withwater through line 8, and this water is removed from the storage spacethrough line 3 controlled by liquid level valve l0, through the agencyof pump II and introduced into the boiler by means of line l2, withauxiliary feed introduced and controlled by some form of boiler waterlevel and feed control as indicated at I3. In the upper portion of thescrubber 3 there is placed a moisture separator I4, of any eflicienttype, such as one of the numerous forms of labyrinth ballle separators,and steam passing through this moisture separator is taken from thescrubber through line I5 to the superheater or to a point of use. Thewater entering through line 8 may be the feed water normally charged tothe boiler, or it may preferably be mixed with increasing proportions ofreturning condensate. For reasons later discussed it is desirable attimes to feed nothing but returning condensate through line 8, so thisline 8 must be understood to be connected to sources of feed water,treated or raw, condensate, and/or other source of water'- low insolid-forming impurities.

The action of the scrubber is as follows: The steam entering the vaporspace between 'water level 6 and partition 4 can escape only by passingunder the lower edge of tube 5 and vertically through that tube into thespace above partition 4. In so passing into tube 5, it entrains liquidsfrom the storage space, the whole passing through tube 5 in a highlycommingled and extremely actively contacting condition whereby each andevery portion of the steam is positively and forcibly contacted withscrubbing medium. Above the partition 4, after exit from the tube 5, inthe relatively enlarged space provided, the water separates from thesteam. Inasmuch as this water is not introduced to the steam underactively steaming conditions in the form of a fine spray, and is usuallyand preferably at a, temchange.

ao'zawe perature somewhat less than that of. the steam, there is verylittle tendency for the steam to carry with it particles of water of asize greater than those which may be separated by an ordinarily' goodmoisture separator placed in location M. I

Figure 2 is a diagrammatic representation of how the apparatusaccomplishing this process may be installed within the steam drum of aboiler. In this figure the function of like parts is the same as inFigure l, and such like parts have been given identical numbers in thetwo figures. v

Due to the reasons pointed out above, the

water carried out of the contacting tube is not difficult to separatefrom the steam, and consequently the installationshown in Figure 2 isfrequently practicable. It may be modified somewhat by installing themoisture remover in an adjacent body, with the contacting tube in thesteam drum.

In'the preferred form of-the process, the installation is according toFigure l, where full requirements of space can be made use of. Thereasons for preference of the outside installation largely arise fromthe moisture separator it. Due to the ability to use all of the spacerequired for the properly designed moisture separator, this moistureseparator is not called upon to work at high rates, and consequently, isnot subject to all of the disadvantages of clo ging, possibility ofre-entrainment of separated moisture and the like, to which a moistureseparator placed in the steaming drum is subject. In addition, it is notcalled upon to separate moisture of the type which must be separated bya baffle in the steaming drum working in serieswith a spray, as thenature and form of the contacting action in tube 5 is such'that therelative size of the moisture droplets is greater than with the sprayand they tend to separate more easily and are additionally enabled toseparate by the possibility, with this process, of being able to scrubthe steam at a point relatively remote from the point' of moistureseparation, as compared to scrubbing it with a spray immediately infront of the baflles in the steaming 'drum.

In steam generatingplants operating at low "boiler pressures, thedifiiculties of solid carryover are frequently not crucial. Similarly,they may be relatively unimportant, if there is an extremelyhighproportion of condensate return to the boiler. The high generatingpressures usual in modern design, in which only a low proportionatereturn of condensate may be possible, requires some other solution ofthe problem. Obviously, a pressure fixed at a high level by the designof the plant is incapable of change thereafter. The net return ofcondensate to the boiler is likewise fixed by the overall conditions of.the installation, and relatively incapable of It is possible, however,by proper operation of my method of steam cleaning, to return enoughcondensate to cleanse the steam, or to obtain the effects of a highrelative pro-. portion of condensate return, in connection with otheradvantages, as will be explained. Advanciently low, then it must bediluted with condensateto attain a concentration of solids sufficientlylow, in the. liquid stored below water level 6, to perform the desiredscrubbing. If there is sufiicient condensate availablethis method may beused. If there is insufficient condensate available to reduce theconcentration of solids in the entire feed water, a third method may beused, in which the feed to the scrubber through line 8 is onlycondensate or predominantly condensate, the main feed to the boilerpassing to the boiler through a separate system. Then this water ofextremely low concentration'is allowed to remain within scrubber 3 untilit has reached a concentration by removal of solids from the steamsuffi-' ciently high that further removal of solids is not practicable.This water is then passed to the boiler through line 9. While in termsand in accomplishment this last method of operation might be consideredto be intermittent, in

actual practice it is continuous, the proportion of drawoff of highlyconcentrated water through line 9, andfeed of condensate or water of lowconcentration through line 8, being so proportloned that theconcentration of the water withcleaning. This may be done by feedingsufficiently cold feed water so that a portion of the steam is condensedwithin the scrubber, thus giving a scrubbing water of. desirably lowconcentration. This method of course does not waste heat, the latentheat of the condensed steam being recovered in the combined condensateand feed which then goes to the boiler.

The efiicacy of this process of steam cleaning is centered around theability to attain positive and complete scrubbing contact of all of theparticles of steam with a scrubbing medium. Collaterally, it isimportant that this scrubbing action be permitted to take place withwater relatively free from impurities which maybe converted to solidsupon evaporation of the water. The requirement of relatively solid-freescrubbing water may be met by scrubbing with condensate obtained fromsubsequent portions of the system, or by use of the feed if that besufficiently solid-free, or by combinations of feed and condensatereturn in various proportions, or by adjusting temperature and amount offeed so that sufiicient condensate isformed within the scrubber itselfto reduce the scrubbing water to the desired solid free degree.

The requirement of intimate and thorough contacting can be attained innumerous ways. For my preferred operation, I make use of the deviceshown in the drawing and described herein, but I do not intend by thisdescription to be limited to the use of this device, but consider anymethod of obtaining such contact to be within the scope of my inventionexcept as limited by the appended claims.

In the diagrammatic drawing attached hereto,

I the contacting of steam and Water is shown as being performed in asingle tube. As a matter of actual practice, it will be preferred to usea plurality oftubes, since requirements of space and efficientcontacting may be more easily met with several tubes 5 of a convenientsize rather than with one large tube of equivalent periphery or ofequivalent cross sectional area. Increases of capacity can consequentlybe made by increasing the number of tubes.

It is to be noted that this method of steam In the previous discussionand theappended claims solids is intended to mean not only solidsactually present within the steam as such, but also is intended toinclude any material capable of appearing as solids at some subsequentpoint in the steam system, such as droplets of highlyconcentratedsolutiomand the like. i

I claim:

1. In a process for removing entrained impurities from steam, the stepswhich comprise liberating steam within a steam generator, removing thesteam from the region in which it was liberated at atemperaturesubstantially that of saturation, maintaining a body of water ofrelatively low content of dissolved solids, intimately contacting thesteam with water from the said body, thereafter separating the waterfrom the steam and returning the water to the body, feeding water tosaid body, withdrawing water therefrom, and proportioning the amount Iand temperature of the feed water to cause a suiiicient condensation ofsteam within the area of contacting to maintain the dissolved solidcontent of the'said body of water below a predetermined maximum, whichis lower than that of the feed water.

2. In a process for removing entrained impurities from steam, the stepswhich comprise liberating steam within a-steam generator, re,- movingthe steam from said steam generating region at a temperaturesubstantially that of 45 saturation, maintaining a body of water ofrelatively low content of dissolved solids, intimately contacting thesteam with water from the said body by passing it through a confinedturbulently flowing stream of water droplets, thereafter sepa- 50 ratingthe water from the steam and returning the water to the body, feedingwater to said body,

withdrawing water therefrom, and proportion-' ing the amount andtemperature of the feed water to cause a suflicient condensation ofsteam within the area or contacting to maintain-the dissolved solidcontent'oi' the said body of water 3. In a process for removingentrained impuriuration, intimately contacting the steam with waterrelatively low in dissolved solids by passing it through a confined,turbulentlyflowing stream of water droplets, said stream being createdand maintained by high velocity contactof said steam with the surface ofsaid body of water adjacent the zone of initiation of said stream, andseparating the steam from the water.-

4. In a process for removingentrained impurities from steam, the stepswhich comprise liberating steam within a steam generator, removing thesteam from the region in which it was liberated at a temperaturesubstantially that of saturation, intimately contacting the steam with,condensate water substantially free from dissolved solids by passing itthrough a confined, turbulently flowing stream of water droplets, saidstream being created and maintained by high veloc ty contact of saidsteam with the surface of sai body of water adjacent the zone ofinitiation of said stream, and separating the. steam from the water. a

5. In a process for removing entrained impurities from steam, the stepswhich comprise liberating steam within a steam generator, removing thesteam from the region in which it was liberated at a temperaturesubstantially that of saturation, maintaining a body of water ofrelatively low content of dissolved solids, intimatelyconta'ctingthesteam with water from the said body by passing it througha confined, turbulently flowing stream of water droplets, said streambeing created and maintained by high velocity contact of said steam withthe surface of said body of water adjacent the zone of initiation ofsaid stream, thereafter separating the water from the steam andreturning'the water to the body, feeding water to said body, withdrawingwater therefrom, and proportioning the amount and temperature of thefeed water to cause a sufficient condensation of steam within the areaof contacting to maintain the dissolved solid content ofthe said body ofwater,below a predetermined maximum.

1 WILLIAM T. SHERMAN.

